The present invention is concerned with a combined Gain-SOA (Semiconductor Optical Amplifier) chip for forming a hybrid laser, and a hybrid laser comprising the combined Gain-SOA Chip.
Hybrid integrated tunable lasers with small line widths, which are increasingly used in optical systems, may comprise an optical output power that is too low for many applications. Such lasers consist of a passive tunable reflector for wavelength selection (e.g. made from silicon, polymer or glass) and an active gain chip (usually an InP chip). In order to increase the optical power, either a separate EDFA (Erbium Doped Fiber Amplifier) or a separate SOA (Semiconductor Optical Amplifier) is coupled downstream [1], which amplifier has to be coupled to the tunable laser in a complicated and precise manner in order to realize a lossless optical coupling.
Conventional approaches, as discussed in [2], suggest integrating a semiconductor optical amplifier on the gain chip used in an external cavity laser. A deeply etched gap between the gain and the SOA section acts as an on-chip mirror. Using such a gain/SOA configuration with a deeply etched gap mirror may achieve the aforementioned desired high output power. However, as the gap width strongly influences the optical coupling losses between the gain and SOA section, very narrow gaps are required and the etching process has to be precisely executed, which leads to an increase in manufacturing costs.
Thus, it would be favorable to have a combined Gain-SOA Chip at hand that can be manufactured in an easier and/or more cost-effective way.